Organometallic polymer and process for production thereof

ABSTRACT

An organometallic polymer of which the main-chain skeleton consists of a Si-CH 2  bond and a V-O bond and which partly contains a vanadiosiloxane bond, the ratio of the number of silicon atoms to that of vanadium atoms being in the range of from 3:1 to 1000:1, the side-chain group directly bonded to the silicon atom being selected from the group consisting of hydrogen, methyl, ethyl and phenyl, and the vanadium atom being bonded to the silicon atom through an oxygen atom with substantially no side-chain organic group present which is directly bonded to the vanadium atom.

BACKGROUND OF THE INVENTION

This invention relates to a novel organometallic polymer partlycontaining a vanadiosiloxane bond (V-O-Si) which has excellent heatresistance and oxidation resistance and a high residual ratio (percentof weight after firing/weight before firing) on firing in anon-oxidizing atmosphere such as nitrogen, argon, helium, ammonia andhydrogen.

Various processes have previously been proposed for the production ofpolycarbosilanes having Si-CH₂ as a main-chain skeleton with an organicside-chain group attached to the silicon atom. For example, Fritzdiscloses a process for production of a polycarbosilane from amonosilane at page 657 of Angew. Chem., 79 (1967). U.S. Pat. No.4,052,430 to Yajima et al. discloses a process for producing apolycarbosilane from a polysilane using an autoclave. Furthermore, U.S.Pat. No. 4,220,600 to Yajima et al. discloses a polycarbosilane partlycontaining a siloxane bond which can be produced by a process which doesnot require an autoclave.

We have now found that a novel organometallic polymer consisting mainlyof carbosilane and partly containing a vanadiosiloxane bond which hasbetter heat resistance and oxidation resistance and a higher residualratio on firing than conventional polycarbosilanes can be obtained byreacting polyvanadiosiloxane or a vanadium complex in which acoordination atom adjacent to the vanadium atom is oxygen, with apolysilane.

SUMMARY OF THE INVENTION

According to this invention, there is provided a novel organometallicpolymer of which the main-chain skeleton consists of a Si-CH₂ bond and aV-O bond and which partly contains a vanadiosiloxane bond, the ratio ofthe number of silicon atoms to that of vanadium atoms being in the rangeof from 3:1 to 1000:1, the side-chain group directly bonded to thesilicon atom being selected from the group consisting of hydrogen,methyl, ethyl and phenyl, and the vanadium atom being bonded to thesilicon atom through an oxygen atom with substantially no side-chainorganic group directly bonded to the vanadium atom.

According to this invention, there is also provided a process forproducing the aforesaid novel organometallic polymer which comprisesmixing polyvanadiosiloxane or a vanadium complex in which a coordinationatom adjacent to the vanadium atom is oxygen, with a polysilane of theformula ##STR1## wherein R₁ and R₂ are identical or different and eachrepresents a member selected from the group consisting of hydrogen,methyl, ethyl and phenyl, provided that R₁ and R₂ are not both hydrogen;and n is a number of not more than 500, and reacting the mixture at atemperature of 250° to 500° C. in a non-oxidizing atmosphere.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is an infrared absorption spectrum chart of the organometallicpolymer of this invention;

FIGS. 2 and 3 are infrared absorption spectrum charts of prior artpolycarbosilanes given for comparison; and

FIG. 4 shows a comparison of the results of the thermogravimetricanalysis of the organometallic polymer of the invention and the priorart polycarbosilane.

DETAILED DESCRIPTION OF THE INVENTION

The process of the invention is first described.

One starting material used in the process of this invention is apolysilane of the formula ##STR2## wherein R₁, R₂ and n are as definedabove. This polysilane may be of a linear or cyclic structure or alinear-cyclic mixed structure. In the above formula, n is usually atleast 3 (n≧3), preferably 5≦n≦100. The sequence of arrangement of thehydrogen, methyl, ethyl and phenyl forming the side-chain groups R₁ andR₂ is optional.

An especially suitable polysilane used in the process of this inventionis polysilane consisting only of a structure of the formula ##STR3## ora polysilane in which at least 50% of the side-chains consists of methyland the remainder being phenyl and/or hydrogen. In the case of linearpolysilanes, the terminal groups are preferably OH or CH₃.

The other starting material used in the process of this invention toreact with the polysilane is polyvanadiosiloxane, or a vanadium complex.

Polyvanadiosiloxane is a polymer which can be produced by the processdisclosed in U.S. patent application Ser. No. 210,639 filed Nov. 26,1980 by Yajima et al., and its main-chain skeleton consists of a Si-Obond and a V-O bond.

The vanadium complex used in the process of this invention is a vanadiumcomplex in which a coordination atom adjacent to the vanadium atom isoxygen. Examples of such a vanadium complex are as follows: ##STR4##

Such a vanadium complex in which a coordination atom adjacent to thevanadium atom is oxygen can be produced, for example by the followingmethods.

(1) By the reaction of an inorganic compound of vanadium with acomplex-forming agent capable of easily forming a complex with theinorganic vanadium compound. Examples of the inorganic compound ofvanadium include vanadium halides such as VCl₄, VCl₃ and VCl₂,oxysulfates of vanadium such as VOSO₄, oxyoxalates of vanadium such asVOC₂ O₄, sulfates of vanadium such as V₂ (SO₄)₃, oxyhalides of vanadiumsuch as VOBr₂, and alkali metal or ammonium salts of the aforesaidcompounds, such as Na(VOCl₄), (NH₄)V(SO₄)₂ and K[VO(C₂ O₄)₂ ]. Examplesof the complex forming agents include C₄ H₈ O(tetrahydrofuran), CH₃ OH,C₅ H₈ O₂ (acetylacetone), C₂ H₅ OC₂ H₅, n-C₄ H₉ OC₄ H₉, (CH₂ OH)₂, CH₃COCH₃, C₅ H₅ OH, C₅ H₄ O₂ (pyrone), C₇ H₆ O (benzaldehyde), C₇ H₆ O₂(benzoic acid) and C₇ H₈ O (benzylalcohol).

Generally, in order to react the vanadium compound with thecomplex-forming agent, it is sufficient only to dissolve the vanadiumcompound in the complex-forming agent with or without heating. In thevanadium complex used in the process of this invention, the vanadiumatom may have an atomic valence of 2, 3, 4 or 5.

A product obtained by dissolving a complex salt of vanadium, such asvanadium acetylacetone complex, in the aforesaid complex-forming agentto react it further may be preferably used in this invention because itsreactivity with the polysilane increases.

(2) By dissolving an organic compound of vanadium such as V₂ OCl₃ (OR)₃,V(OR)_(n), VO_(x) (OR)_(4-x) (wherein R is C₁ -C₄ alkyl, n is 3, 4, or 5and x is 1 or 2), VCl(OCH₃)₂, and VOCl₂ (OC₂ H₅) in a lower alcohol suchas methanol, ethanol, n-propanol, iso-propanol, n-butanol, sec-butanoland t-butanol, the vanadium complex used in this invention can also beproduced.

According to the process of this invention, the organometallic polymeris produced by mixing the polyvanadiosiloxane or the vanadium complex inwhich a coordination atom adjacent to the vanadium atom is oxygen, withat least one polysilane of the formula ##STR5## and heating the mixtureat 250° to 500° C. in a non-oxidizing atmosphere to performpolymerization.

It is necessary that the heating should be carried out in anon-oxidizing atmosphere. If the polymerization reaction is carried outin an oxidizing atmosphere such as air, oxidation of the startingpolysilane takes place so that the reaction does not sufficientlyproceed. Nitrogen, argon, hydrogen and ammonia are suitable as thenon-oxidizing atmosphere inert to the reaction. Nitrogen, argon andhelium are especially preferred because of their good ability to behandled.

Preferably, the polymerization reaction is carried out generally atatmospheric pressure or pressures close to it. If the polymerizationreaction is carried out in vacuum or at highly reduced pressures,low-molecular components distill out of the reaction system to reducethe yield of the product drastically. Furthermore, it is preferred thatthe polymerization reaction in the process of this invention be carriedout while introducing the nonoxidizing gas at a fixed flow rate into thereactor. This is because by so doing, the pressure in the reactionvessel can be maintained nearly at atmospheric pressure, and a rise intemperature, or a rise in pressure owing to gases such as methanereleased during the reaction, can be avoided.

The heating temperature in the process of this invention is usually 250°to 500° C. If the reaction temperature is below 250° C., thepolymerization does not easily proceed, and if the temperature exceeds500° C., the resulting organometallic polymer begins to becomeinorganic, (namely, liberation of side-chain components graduallybegins).

The ratio between the polysilane and the vanadium compound(polyvanadiosiloxane or the vanadium complex) is determined so that theratio of the number of silicon atoms to that of vanadium atoms in thefinal organometallic polymer is within the range of 3:1 to 1000:1.

The time required for the heat polymerization in the process of thisinvention is usually 1 to 10 hours, and the reaction substantially comesto an end within 10 hours.

Practice of the process of this invention requires only a simple reactorincluding a reflux device, etc., and no special device such as apressurized vessel or a flowing-type device capable of permittingrecycling is required.

The organometallic polymer obtained by the aforesaid polymerization canbe purified by dissolving it in a solvent such as n-hexane, benzene,xylene or tetrahydrofuran, filtering it, and evaporating the solventfrom the filtrate. If required, the purified product may further bedistilled and concentrated under atmospheric pressure or under reducedpressure at a temperature of 50° to 450° C.

A description of the organometallic polymer obtained by the aboveprocess and partly containing a vanadiosiloxane bond follows.

The organometallic polymer obtained in hereinbelow Example 1 frompolydimethylsilane as the starting polysilane shows an infraredabsorption spectrum given in FIG. 1. For comparison, an infraredabsorption spectrum of polycarbosilane synthesized by treatingpolydimethylsilane in an argon atmosphere at 470° C. and 36 atmospheresfor 36 hours in an autoclave in accordance with the method disclosed inU.S. Pat. No. 4,052,430 to Yajima et al. is shown in FIG. 2.Furthermore, FIG. 3 shows an infrared absorption spectrum ofpolycarbosilane partly containing a siloxane bond obtained by mixing 250g of polydimethylsilane with 10 g of polyborodiphenylsiloxane, heatingthe mixture to 370° C. in a nitrogen stream and polymerizing it for 5hours, by the method disclosed in U.S. Pat. No. 4,220,600 to Yajima etal.

The infrared absorption spectrum given in FIG. 1 shows absorptions ofC-H at 2950 cm⁻¹ and 2900 cm⁻¹, Si-H at 2100 cm⁻¹, Si-CH₃ at 1260 cm⁻¹and 800 cm⁻¹, and Si-CH₂ -Si at 1040 cm⁻¹, and also exhibits newabsorption peaks at 3400 cm⁻¹, 1600 cm⁻¹, 1180 cm⁻¹, 960 cm⁻¹, 880 cm⁻¹,740 cm⁻¹, and 490 cm⁻¹ ascribable to the Si-O-V bond. These newabsorption peaks are not seen in the infrared absorption spectra of thepolycarbosilane in FIG. 2 and the polycarboxilane partly containing asiloxane bond in FIG. 3.

Observation of the novel organometallic polymer obtained in Example 1with an electron microscope showed that no crystal grain is present inits bright field image. The results of measurements by powder X-raydiffraction and electron beam diffraction showed no formation of solidvanadium oxide. These experimental data led to the determination thatsubstantially all of the vanadium atoms are involved in the Si-O-V bond.

A particular difference of the organometallic polymer of this inventionfrom conventional polycarbosilanes is that its main-chain skeletonconsists of an Si-CH₂ bond and a V-O bond, and when it is fired in anonoxidizing atmosphere, crosslinking through the vanadiosiloxaneportion proceeds further at 300° to 350° C. to increase its crosslinkingdensity and inhibit heat decomposition of the organometallic polymer,and therefore its residual ratio on firing is high. This fact is clearlyshown by the results of thermogravimetric analysis described in FIG. 4.Curve (A) in FIG. 4 is a thermogravimetric curve of the organometallicpolymer obtained in Example 1, and curve (B) is a thermogravimetriccurve of polycarbosilane partly containing a siloxane bond produced bythe method described in U.S. Pat. No. 4,220,600 to Yajima et al.

The structure of the organometallic polymer of this invention iscomplex, and complete elucidation of its exact structure is impossibleaccording to the present technical level of chemistry. The presentinventors, however, presume that it has partial structures exemplifiedhereinbelow. ##STR6##

(In the above formulae, R is at least one member selected from the groupconsisting of methyl, ethyl, phenyl and hydrogen.)

In the above exemplification of the partial structures of theorganometallic polymer with a main chain skeleton consisting of anSi-CH₂ bond and a V-O bond, a trivalent or tetravalent vanadium atom isbonded to the silicon atom through an oxygen atom. Generally, in theorganometallic polymer of this invention, the stable atomic valence ofthe vanadium atom is trivalent or tetravalent, but a divalent vanadiumatom could exist.

Powder X-ray diffraction analysis of the organometallic polymer of thisinvention has shown it to be amorphous as are conventionalpolycarbosilanes. When the polymer is fired in a non-oxidizingatmosphere such as argon, helium, hydrogen, ammonia and nitrogen gas, itis converted mainly to β-SiC containing vanadium. When a fired productobtained by firing the novel organic organometallic polymer (obtained inExample 1) in an argon stream at 1400° C. for 1 hour is analyzed bypowder X-ray diffraction using a nickel filter and a Cu target as anX-ray source, β-SiC and graphite are mainly identified. Vanadium isdetected from the resulting product by a wet colorimetric method.

From the results of elemental analysis of the organometallic polymerobtained by this invention, the weight percentages of the individualelements in the polymer are generally as follows:

Si: 30-60, C: 20-60, O: 0.5-3, H: 5-10,

V: 0.01-15% by weight

The results of measurement of the molecular weight distribution of thepolymer by G. P. C. show that the polymer has a molecular weightdistribution in the range of 500 to 100,000, and its number averagemolecular weight, measured by the vapor pressure method, is 1400 to2200.

The organometallic polymers in which the main-chain skeleton consists ofan Si-CH₂ bond and a V-O bond are thermoplastic substances, which aresoluble in organic solvents such as n-hexane, xylene, tetrahydrofuranand benzene, and melt by heating to 60° to 300° C. Hence, they can bemolded using various aggregates by utilizing an ordinary monoaxialpress, isostatic press, injection press, etc. or by extrusion molding.The molded article is fired in a non-oxidizing atmosphere at atemperature of at least 800° C. to convert a part of the binder to aninorganic carbide SiC. Alternatively, a sintered molded article may beobtained by impregnating an inorganic fired article prepared separately,with a molten mass of the organometallic polymer of the inventionobtained by heating in a non-oxidizing atmosphere, or a solution of theorganometallic polymer of the invention in an organic solvent, andfiring the impregnated molded article at 1300° to 1800° C. in anon-oxidizing atmosphere, whereby the pores in the inorganic firedarticle are filled with SiC.

The novel organometallic polymer of the invention whose main-chainskeleton consists of an Si-CH₂ bond and a V-O bond and which partlycontains a vanadiosiloxane bond and has excellent heat resistance andoxidation resistance is very advantageous for forming continouousfilaments, films, coated films and powders composed mainly of siliconcarbide because its residual ratio on firing in a non-oxidizingatmosphere is high.

Table 1 below summarizes the properties of the novel organometallicpolymer partly containing a vanadiosiloxane bond shown in Example 1 incomparison with those of polycarbosilane synthesized frompolydimethylsilane in an autoclave at 470° C. for 14 hours with thefinal pressure in the vessel being 110 atmospheres in accordance withthe method disclosed in U.S. Pat. No. 4,052,430, and polycarbosilanepartly containing a siloxane bond which is synthesized frompolydimethylsilane and 3.85% by weight of polyborodiphenylsiloxane at400° C. for 5 hours in a nitrogen atmosphere in accordance with themethod disclosed in U.S. Pat. No. 4,220,600.

                  TABLE 1                                                         ______________________________________                                                                Polycarbo-                                                                    silane                                                                        partly                                                                        containing                                                                              Novel                                                               a siloxane                                                                              organo-                                                 Polycarbosilane                                                                           bond (U.S.                                                                              metallic                                                (U.S. Pat.  Pat. No.  polymer                                     Properties  No. 4,052,430)                                                                            4,220,600)                                                                              (Example 1)                                 ______________________________________                                        Number average                                                                            1800        1720      1900                                        molecular weight                                                              Decomposition                                                                             310         350       370                                         temperature (°C.)                                                      Weight increase (%)                                                           owing to oxidation                                                            after maintaining                                                                         9.0         6.5       6.0                                         at 200° C. for 1                                                       hour in the air                                                               Residual ratio (%)                                                            on firing                                                                     (after maintaining                                                                        49.8        73.8      75.0                                        at 1500° C. in argon                                                   gas for 1 hour)                                                               ______________________________________                                    

The results given in Table 1 show that the organometallic polymer ofthis invention has improved properties over prior art polycarbosilanes.

The following Examples illustrate the present invention.

EXAMPLE 1

40 ml of a solution of 25 g of VCl₄ in 500 ml of tetrahydrofuran wasadded to 20 g of a,w-dihydroxypolydimethylsiloxane having an averagedegree of polymerization of 500 in a beaker. The beaker containing theabove mixture was heated on a hot plate at 190° C., and the heating wasstopped when the mixture became highly viscous. The mixture was thenhot-filtered, and tetrahydrofuran was added to the filtrate so that thetotal amount of the mixture reached 100 ml.

Twenty grams of polydimethylsilane of the formula ##STR7## was weighedinto a 200 ml bulb-shaped flask, and 100 ml of the above tetrahydrofuransolution was added. They were stirred in a nitrogen atmosphere, and themixture was heated to 200° C. from room temperature so as to evaporatethe tetrahydrofuran.

Then, a reflux condenser was attached to a 100 ml. bulb-shaped flask,and the bottom of the flask was kept at 400° C. in a nitrogenatmosphere. The reaction was performed by heating with an electricfurnace, and the reaction mixture was maintained at 400° C. for 5 hours.

After the reaction, xylene was added, and the solution was filtered atatmospheric pressure. The filtration product was transferred to a 200 mlroundbottomed separable flask, and a Liebich condenser was attached tothe flask for distillation. With stirring, nitrogen gas was passedthrough the flask, and the product was heated from room temperature by amantle heater.

By heating, xylene was distilled at the boiling point (140° C.) ofxylene, and then the temperature was slowly raised up to 320° C. at arate of 10° C./10 minutes to remove a low-molecular-weightorganometallic polymer, and concentrate the product.

The above procedure gave 12 g of a concentrate. Its infrared absorptionspectrum was measured, and the results are shown in FIG. 1.

The organometallic polymer was subjected to elemental analysis, and theresults were as follows:

Si: 50% by weight

C: 38% by weight

H: 6% by weight

O: 4.8% by weight

V: 1.0% by weight

When the organometallic polymer was fired in an atmosphere of argon fromroom temperature to 1500° C., its residual ratio on firing was 75%.Powder X-ray diffraction (CuKα,Ni filter) of the fired product led tothe determination that the fired product consisted mainly of β-SiC, andα-SiC and graphite were also identified. Vanadium was detected from thefired product by a wet colorimetric method.

The organometallic polymer was found to have a molecular weightdistribution, measured by GPC, of from 500 to 100,000. The polymer wasalso found to have a number average molecular weight, measured by thevapor pressure method, of 1900.

EXAMPLE 2

In a 100 ml bulb-shaped flask, 40 g of the same polydimethylsilane asused in Example 1 was mixed with 15 ml of a VCl₄ /tetrahydrofurancomplex obtained by dissolving 25 g of VCl₄ in 500 ml oftetrahydrofuran.

A rotary evaporator was attached to the bulb-shaped flask, and thetetrahydrofuran was evaporated at a water bath temperature of 60° C. anda pressure of 50 mmHg produced by a water flow pump. Then, the sameprocedure as in Example 1 was repeated to give an organometallicpolymer. The polymer was filtered and concentrated to give 26 g of afinal product.

The resulting final organometallic polymer was heated from roomtemperature to 1400° C. at a rate of 5° C./min. The heated product wasthermogravimetrically analyzed. It was found that the residual ratio onfiring was 65%.

EXAMPLE 3

A solution of 6.5 g of vanadyl sulfate (VOSO₄) in 100 cc ofacetylacetone was well mixed with 50 g of polysilane in which the ratioof methyl groups/phenyl groups in the side chain was 70:30. Theacetylacetone was evaporated by distillation. Then, the dry powder wasput into a three-necked flask equipped with a stirrer, and in a streamof argon, the bottom of the flask was heated to 500° C. to melt it.Then, it was polymerized for 10.5 hours.

The polymer was dissolved in tetrahydrofuran, and filtered. Then,tetrahydrofuran was evaporated in a stream of nitrogen, and the residuewas then concentrated at 350° C. for 1 hour.

The resulting organometallic polymer had a number average molecularweight of 2013, and when it was fired at 1700° C. for 1 hour in a streamof argon, the residual ratio on firing was 70%.

EXAMPLE 4

100 g of polydimethylsilane (degree of polymerization 50) and 3 g ofvanadyl oxalate (VOC₂ O₄) in 50 cc of tetrahydrofuran were mixed in astream of argon. The tetrahydrofuran was evaporated by distillation.Then, the mixture was bubbled with nitrogen gas in a stream of nitrogenin a reactor equipped with a reflux condenser, and then polymerized at370° C. for 6.0 hours.

The polymer was heated from room temperature to 1400° C. in a stream ofargon, and a change in weight was measured. The residue was 72%. PowderX-ray diffraction analysis of the fired product led to theidentification of β-SiC and graphite.

What we claim is:
 1. An organometallic polymer of which the main-chainskeleton consists of a Si-CH₂ bond and a V-O bond and which partlycontains a vanadiosiloxane bond, the ratio of the number of siliconatoms to that of vanadium atoms being in the range of from 3:1 to1000:1, the side-chain group directly bonded to the silicon atom beingselected from the group consisting of hydrogen, methyl, ethyl andphenyl, and the vanadium atom being bonded to the silicon atom throughan oxygen atom with substantially no side-chain organic group presentwhich is directly bonded to the vanadium atom.
 2. The organometallicpolymer of claim 1 which melts when heated to 60° to 300° C.
 3. Theorganometallic polymer of claim 1 which is soluble in organic solvents.4. A process for producing the organometallic polymer of claim 1 whichcomprises mixing polyvanadiosiloxane or a vanadium complex in which acoordination atom adjacent to the vanadium atom is oxygen, with apolysilane of the formula ##STR8## wherein R₁ and R₂ are identical ordifferent and each represents a member selected from the groupconsisting of hydrogen, methyl, ethyl and phenyl, provided that R₁ andR₂ are not both hydrogen; and n is a number of not more than 500, andreacting the mixture at a temperature of from 250° C. to 500° C. in anon-oxidizing atmosphere.